137
free solvent, SWE is becoming the most sorted technique for extracting pectin
(Ueno et al. 2008).Also the GRAS status of solvent being employed, the technique
finds more usage in food and agro based industries. However the process needs to
be standardised and kept in control owing to the susceptibility of the pectin chains
to degradation (Khajavi et al. 2005). Also the cost considerations prove to be a hindrance for using this technique on commercial scale. Various factors play a key role
in governing the extraction yield in case of SWE and these include: temperature,
time, pressure, particle size etc. For temperatures as high as 170 °C, investigations
have been done to study the effect of such high temperatures on extracting pectin.
Another important factor that must be taken into consideration during optimization
of the process is time, as the long duration process may result in the degradation of
the pectin chains. Pressure not only keeps the water away from changing its phase
but also affects the yield of pectin. This factor has been studied by Chen et al. (2015)
and others who investigated SWE at pressures up to 10 MPa. The yield of pectin can
also be influenced by particle size of the parent material.
Ultra Sound Assisted Extraction (UAE)
Ultra sound waves are the sound waves having frequencies from 20 kHz to1–16 kHz.
A major difference between ultra sound and electromagnetic waves is that ultrasound waves require a medium (solid, liquid or gas) for their propagation. This
involve cycles of expansion and compression and while passing through the liquid
medium, these lead to the formation and collapse of bubbles, that ultimately result
in the formation of microjets. This phenomenon through which these bubbles grow
and collapse is known as cavitation. The process of cavitation can last for 400 ms
and within this, high temperatures and pressures about 5000 °C and 1000 atm can
be attained (Luque-Garcıa and Luque de Castro 2003). These high-speed jets and
waves are then used to swell the materials because of the intermixing of solvents
and pore enlargement. This also increases the molecular mobility and subsequently
increases the yield. It has been reported that an increase beyond the 65 W can
increase the bubble formation which can decrease the ultrasound energy transmitted
into the system. As the ultrasound can break down the polymers, so it can have
implications on physicochemical properties of pectin side chains of the pectin molecules are more prone to the degradation by ultrasound and is witnessed by the fact
that there is reduction in the (Gal + Ara/Rha) ratio which corresponding to the neutral side chains. Again the increased intensity and time duration decreased the ratio.
Zhang et al. (2013) reported negative effects on the gelling properties of the sonicated pectin. Pectin gel in such a case was reported to have weak molecular structure but were more transparent. Also the rate of gelation decreased with the
increasing intensity and time of ultrasonication. Of course, UAE has a number of
advantages such as it reduces the extraction time, lowers the usage of solvent and
also saves the energy. Many workers have also reported this technique in being most
effective for mixing and micromixing, for having higher mass and energy transfer
rates most notably reducing the concentration gradients and extraction temperature.
Pectin
free solvent, SWE is becoming the most sorted technique for extracting pectin
(Ueno et al. 2008).Also the GRAS status of solvent being employed, the technique
finds more usage in food and agro based industries. However the process needs to
be standardised and kept in control owing to the susceptibility of the pectin chains
to degradation (Khajavi et al. 2005). Also the cost considerations prove to be a hindrance for using this technique on commercial scale. Various factors play a key role
in governing the extraction yield in case of SWE and these include: temperature,
time, pressure, particle size etc. For temperatures as high as 170 °C, investigations
have been done to study the effect of such high temperatures on extracting pectin.
Another important factor that must be taken into consideration during optimization
of the process is time, as the long duration process may result in the degradation of
the pectin chains. Pressure not only keeps the water away from changing its phase
but also affects the yield of pectin. This factor has been studied by Chen et al. (2015)
and others who investigated SWE at pressures up to 10 MPa. The yield of pectin can
also be influenced by particle size of the parent material.
Ultra Sound Assisted Extraction (UAE)
Ultra sound waves are the sound waves having frequencies from 20 kHz to1–16 kHz.
A major difference between ultra sound and electromagnetic waves is that ultrasound waves require a medium (solid, liquid or gas) for their propagation. This
involve cycles of expansion and compression and while passing through the liquid
medium, these lead to the formation and collapse of bubbles, that ultimately result
in the formation of microjets. This phenomenon through which these bubbles grow
and collapse is known as cavitation. The process of cavitation can last for 400 ms
and within this, high temperatures and pressures about 5000 °C and 1000 atm can
be attained (Luque-Garcıa and Luque de Castro 2003). These high-speed jets and
waves are then used to swell the materials because of the intermixing of solvents
and pore enlargement. This also increases the molecular mobility and subsequently
increases the yield. It has been reported that an increase beyond the 65 W can
increase the bubble formation which can decrease the ultrasound energy transmitted
into the system. As the ultrasound can break down the polymers, so it can have
implications on physicochemical properties of pectin side chains of the pectin molecules are more prone to the degradation by ultrasound and is witnessed by the fact
that there is reduction in the (Gal + Ara/Rha) ratio which corresponding to the neutral side chains. Again the increased intensity and time duration decreased the ratio.
Zhang et al. (2013) reported negative effects on the gelling properties of the sonicated pectin. Pectin gel in such a case was reported to have weak molecular structure but were more transparent. Also the rate of gelation decreased with the
increasing intensity and time of ultrasonication. Of course, UAE has a number of
advantages such as it reduces the extraction time, lowers the usage of solvent and
also saves the energy. Many workers have also reported this technique in being most
effective for mixing and micromixing, for having higher mass and energy transfer
rates most notably reducing the concentration gradients and extraction temperature.
Pectin